a) Field of the Invention
The present invention relates generally to disk drives comprising thin film magnetic transducers and, in particular to improvements in such transducers and their electrical connection in the drives for preventing capacitive coupling between the magnetic pole tips of the transducers and adjacent disks.
b) Background Art
In current computer technology, the common mass storage device is a hard disk drive wherein data is stored on disks as magnetic patterns on a thin film of magnetic material on the surface of the disk. The data is recorded and read by the thin film magnetic transducer or "head". Within the magnetic thin film transducer is a magnetic circuit comprising a thin film pole structure which is wrapped around or encircles the turns of a flat, spirally wound coil. The thin film pole structure comprises spaced pole tips beyond the outer periphery of the coil, defining a magnetic gap therebetween. The transducer is positioned so that the pole tips scan a disk surface as the disk rotates. The coil is connected in an amplifier circuit which maintains the coil at a potential above the potential of the disks, usually 5 volts. The coil is insulated from the magnetic circuit with a photo-resistive material which is ideally a high resistance insulator, but may have portions with poor insulating qualities due to imperfections, such as tiny holes in the photo-resistive material or extraneous pieces of metal left on the photo-resistive material during processing which capacitively couples the coil to the pole tips. There is therefore, often a charge present on the pole tips of the transducer. A problem occurs when the transducer comes near a peak or other anomaly on the disk and discharges occur from the pole tips to the disk. Electrical discharge from the pole tips of the transducer to the disk can destroy a thin film transducer. Further, the noise created by a less than damaging electrical discharge can cause errors in reading data from the disk. In addition, there are always displacement currents due to variable capacitive coupling between the pole tips and the grounded disk. Electrostatic shielding and elimination of the potential difference between the pole tips and the thin film metallic disk is therefore needed to prevent the introduction of noise into the disk drive electronics.
One method of avoiding this problem has been to apply a bias voltage to the disk which is equal to the amplifier voltage on the transducer, thereby placing the disk and the transducer at the same potential. One advantage to this technique is that any transducer can be used with the disk being charged to meet the potential of the transducer. However, this adds complexity in disk drive manufacturing and the resultant possibility of poor yields and high component costs.
U.S. Pat. No. 4,317,149 to Elser et al discloses a magnetic head assembly having conductive strips that function as bypass paths to discharge static electrical charges at a distance from the effective magnetic pole pieces and transducing gap.
U.S. Pat. No. 4,761,699 to Ainslie et al teaches a method for attaching a slider to a suspension in a data recording disk file using reflowed solder balls instead of epoxy binding to avoid static discharge from the pole tips of the transducer to the disk.
U.S. Pat. No. 4,800,454 to Schwarz et al discloses a method of static charge protection for magnetic thin film transducers which uses a conductor which makes electrical contact with the flyer body and with the magnetic core to prevent electrostatic discharge between the flyer body and the pole tip. An opening is formed in the insulating layer between the thin film transducer and the conducting substrate.
A problem occurs with this technique of static charge protection in that the flyer body is mildly conducting so that a charge can build up and subsequently discharge from the pole tip to the disk. A problem is also presented by the requirement in Schwarz et al of forming an opening in the insulating layer between the flyer body and the magnetic core which requires going through up to 10 microns of Al.sub.2 O.sub.3 which is difficult to penetrate and requires additional processing steps in forming the transducer, which effects the yield.